Recent generation mobos allow SSDs either to cache for a HDD or as boot medium on its own. If you haven't started with a SSD with the operating system on it from new, and you haven't got disks for the OS, is it trouble to move your OS (assuming we're talking WIndows) from the HDD to the SSD?
Is the moral just to get the SSD to start with and are they worth the current premium, given that HDD prices are high now anyway, or to go for a free OS so you can always get a free copy when you need it?